The blockage of an arterial vessel produces ischemia in the tissue normally nourished by the occluded vessel. If the blockage is removed permitting reperfusion of the affected area after greater than sixty minutes of ischemia, further injury called reperfusion injury is paradoxically observed. This reperfusion injury is associated with a number of biochemical and physiological events such as release of intracellular enzymes, transient rise in blood pressure, reduction in contractility, influx of calcium, disruption of cell membranes, and eventual tissue necrosis (see Ferrari, et al., Am. J. Clin. Nutr. 53:215S (1991). It is thought that much of the tissue damage arising during ischemia and reperfusion results from the chemical action of excess amounts of oxygen free radicals which have accumulated (Lefer, et al., Basic Res. Cardiol., 86 Suppl. 2:109 (1991) and Kirsh, et al., J. Neurotrauma, 9 Suppl. 1:S157 (1992), and Bolli, Cardiov. Drugs & Ther., 5:249 (1991).
Experiments in a number of animal models have investigated the use of antioxidants or enzymes to control reperfusion injury. For example, Weyrich, et al., Circulation, 86:279 (1992) showed that administration of L-arginine reduced necrotic injury in a cat model of myocardial infarction. McMurray et al., J. Clin. Pharmac., 31:373 (1991) investigated sulfhydryl containing angiotensin converting enzyme inhibitors. Naslund, et al., Circ. Res., 66: 1294 (1990) concluded from their work on a swine coronary model, that infarct size could by limited by administration of superoxide dismutase, but only during a very narrow window of time post-infarction. Schaer, et al., JACC, 15:1385 (1990) report a reduction in reperfusion injury by administering an acellular oxygenated perfluorochemical emulsion called Fluosol.
An important model system is percutaneous transluminal coronary angioplasty in the pig. McKenzie, et al., Biomat., Art., Cells & Immob. Biotech., 20:2 (1992) utilized this technique to study the effects of temporary regional myocardial ischemia. They inserted a catheter into the proximal left anterior descending coronary artery and inflated the catheter balloon to occlude the artery for a period of 4 minutes. A significant reduction in cardiac function is reported compared to controls as measured by mean arterial blood pressure (MAP), peak systolic left ventricular pressure (IVP), rate of left ventricular pressure development (dP/dt), pressure rate product (PRP), and cardiac output (CO). In addition, electrocardiograms showed depression of the S-T segment of the ECG. These experiments are significant because McKenzie, et al. compared controls to animals receiving infusions of hemoglobin, and found that cardiac function and S-T segment ECG both increased significantly.
The concept of infusing hemoglobin products as a substitute for blood has a long history (for a historical perspective, see R. M. Winslow, "Hemoglobin-based Red Cell Substitutes", The Johns Hopkins University Press, 1992). Free hemoglobin is not suitable for this purpose since oxygen is bound too tightly to be released in the tissues. Also, hemoglobin monomers are rapidly cleared from the blood and exhibit renal toxicity. Better success has been achieved with chemically modified hemoglobins, which assume a conformation allowing release of oxygen, and whose size and stability are more resistant to clearance.
Hemoglobins may be alpha alpha crosslinked as disclosed in U.S. Pat. Nos. 4,600,531 and RE 34,271 (Walder), and virus inactivated and purified as taught in U.S. Pat. No. 4,861,012 (Estep). Modification by pyridoxyation, carbamylation, carboxymethylation, are also known, as are chemical schemes for both cross-linking and polymerizing, as by glutaraldehyde. A summary of these chemistries is contained in Winslow, supra.